This invention generally relates to catheters, and particularly to intravascular catheters for use in percutaneous transluminal coronary angioplasty (PTCA) or for the delivery of stents.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced in the patient's vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. A dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with inflation fluid one or more times to a predetermined size at relatively high pressures so that the stenosis is compressed against the arterial wall and the wall expanded to open up the vascular passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand the artery wall. After the balloon is finally deflated, blood resumes through the dilated artery and the dilatation catheter and the guidewire can be removed.
In such angioplasty procedures, there may be restenosis of the artery, i.e., reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate of angioplasty alone and to strengthen the dilated area, physicians may implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel or to maintain its patency.
Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded within the patient's artery to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. For details of stents, see for example, U.S. Pat. No. 5,507,768 (Lau, et al.) and U.S. Pat. No. 5,458,615 (Klemm, et al.), which are incorporated herein by reference.
An essential step in effectively performing a PTCA procedure is properly positioning the balloon catheter at a desired location within the coronary artery. To properly position the balloon at the stenosed region, the catheter must have good pushability (i.e., ability to transmit force along the length of the catheter), and good trackability and flexibility, to be readily advanceable within the tortuous anatomy of the patient's vasculature. Conventional balloon catheters for intravascular procedures, such as angioplasty and stent delivery, frequently have a relatively stiff proximal shaft section to facilitate advancement of the catheter within the patient's body lumen and a relatively flexible distal shaft section to facilitate passage through tortuous anatomy such as distal coronary and neurological arteries without damage to the vessel wall. These flexibility transitions can be achieved by a number of methods, such as bonding two or more tubing segments of different flexibility together to form the shaft. However, such transition bonds must be sufficiently strong to withstand the pulling and pushing forces on the shaft during use. At present, however, there are distinct shortcomings associated with the methods of manufacture proposed to produce a catheter with this characteristic. In particular, current methods do not satisfy the necessary tensile strength requirements set for such devices.
One proposed method of creating a varying stiffness catheter involves cutting segments of different multi-layer tubular members and joining them together end to end, with the outermost layer of the distal segment(s) having a reduced durometer and/or thickness compared with that of its adjacent more proximal segment. While this technique was used to produce samples which were bench tested to prove the merit of the technology with regard to deliverability, the joints created by the mating of the segments were not sufficiently robust to meet product tensile strength and other reliability requirements. The reason for this is that most catheter tubings are multi-layers, such as tri-layer extrusions. These three-layer configurations have an innermost layer that is particularly difficult to join end-to-end, because the innermost layer is typically constructed of high density polyethylene (HDPE), which is not melt-bond compatible with a nylon or Pebax outermost layer. Attempts to either butt-join or lap-join tri-layer inner member segments have been unsuccessful because all abutting or overlapping layers did not bond reliably to one another.
Past approaches to improve joint reliability and overall manufacturability have all suffered several common drawbacks: the tubing needed to be heated along its entire length to bond the various pieces together; and an entire length of shrink tubing covering the length of the tubing must be used to bond the layers and then discarded. For rapid exchange balloon catheters and other catheters, where the variable stiffness tubing spans approximately 25 cm within the finished device, the extended shrink tubing amounts to a considerable overall cost increase (multiple extrusions, shrink tubing, more direct labor required for assembly) relative to a conventional tri-layer extrusion. For over the wire balloon catheters, in which the variable stiffness tubing can be approximately five times longer, the cost becomes essentially prohibitive.